Role of Alkalis and Sulfates of Portland Cement on Durability of Florida Structures

摘要

In this study, several ASTM Portland cements were used to address the effects of increasing alkali and sulfur trioxide content of cements on performance and durability of concrete. Several characterization techniques were used including: x-ray diffraction, x-ray spectroscopy, scanning electron microscopy, calorimetric studies, fineness, and porosomistry. Several curing regimes were employed that include ambient curing and elevated temperature curing. Two exposure environments were used; namely, lime and marine solution. The findings indicate that increasing sulfur trioxide content increases expansion in lime due to an increase in ettringite formation. Increasing the alkali content was well tolerated, in terms of expansion, if the curing temperature was at 23 degrees C and the exposure solution was lime. Strength loss was found to occur on increasing the alkali content, under ambient conditions and lime exposure, for all sulfate levels. Strength loss accompanying increase in alkali content can be as high as 4,000 psi. Strength regression with increasing alkali content was found to depend on cement mineralogy. Increasing the curing temperature to 80o C increased expansion. The amount of expansion was found to depend on cement mineralogy with the highest expansion recorded for cements of high tricalcium silicate and aluminate content.